Gas purification process



March 1949- H. A. GOLLMAR GAS PURIFICATION PROCESS Filed Feb. 20, 1945mv 0 l 3. 0V 3 mm mm mm mm 0% IN VENT OR.

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' Patented Mar. 22, 1949 UNITED STATES PATENT OFFICE GAS PURIFICATIONPROCESS Herbert A. Gollmar, Mount Lebanon, Pa., assignor to KoppersCompany,.1nc., Pittsburgh, Pa., a corporation of Delaware ApplicationFebruary 20, 1945, Serial No. 578,861

collecting mains.

An efiective process for the purification of coke-oven gas in respect ofits hydrogen sulphide content and for the recovery of the hydrogensulphide comprehends scrubbing the gas with an alkaline aqueoussolution; absorbing therein hydrogen sulphide; thereafter activating thealkaline solution for further absorption use by heating it under lessthan atmospheric pressure and thereby boiling and sweeping out hydrogensulphide; and condensing moisture from the recovered hydrogen sulphide.Similar processes comprise removal of hydrogen cyanide, ammonia, lightoil, or other compounds from coke-oven gas with a liquid absorbent andsubsequent reactification of the absorbent under vacuum.

A primary object of the present invention is the provision of a moreeconomical process of the type outlined above for liquid purification ofcoke-oven gas or of other fluid product of a cokeoven such as light oil.and the recovery of hydrogen sulphide or other constituent therefrom.

Another object of the invention is to provide a process of liquidpurification which is more closely articulated with the byproduct systemof I a coke plant in order that overall advantages of economicaloperation can be obtained.

The invention has for further objects such other improvements and suchother operative advantages or results as may be found to obtain in theprocesses or apparatus hereinafter described and claimed.

The present improvement contemplates utilizing for suchvacuum-actification. as is abovedescribed. the low-temperature heat thatis present in thefluid, both liquidous and gaseous, eiliuent of thecollecting mains of a coke-oven battery. The heat in these fluids is atsuch low thermal head that ordinarily ithas been wasted since it has notbeen thought to be at a suillciently high temperature level forbyproduct processes requiring heat. It has been the custom heretofore toemploy special cooling means to cool the fluids to desired temperature.The gas purification process of instant reference is particularly 3Claims. (Cl. 23-3) well adapted to the present improvement since thedescribed waste heats can be used effectively under the vacuum in theaetification zone even though the heats are of such low thermal head.

.In addition, the removal of heat from the said fluids for actificationpurposes at the same time efi'ects the desired cooling of the efliuentfluid.

As a specific improvement also within the teaching of the presentinvention, the utilization of heat from coke-oven gas is described andclaimed in copending application Serial No. 545,468, filed July 18,1944, now Patent No. 2,379,076.

In the accompanying drawing forming a part of this specification andillustrating for purposes oi exemplification a preferred apparatus andmethod in which the invention is embodied and practiced but withoutlimiting the claimed invention specifically to such illustrativeinstance or instances; the single figure is a diagrammatic elevationalview of apparatus for the liquid puriflcation of gas utilizing the heatof coke-plant flushing liquor.

Referring to the figure, coke-oven gas containing hydrogen sulphideflows through a pipe 2 into an absorber 4 containing packing and inwhich the said gas rises in countercurrent contact with continuouslydescending absorbent, for example, an alkaline aqueous solutioncontaining sodium carbonate and sodium acid carbonate.

The said sodium carbonate solution in the absorber 4 absorbs hydrogensulphide from the countercurrently flowing coke-oven gas. The so-treatedcoke-oven gas leaves the absorber at the top thereof and flows toadditionalapparatus of the byproduct system through the pipe 8.Fouled-absorbent solution flows from the bottom of the absorber 4through a valved pipe 8 into a pumping tank III to which also isdelivered through a valved pipe l2 freshly made up absorbent; The saidmade up absorbent is prepared-in a mixing tank l'4 into which isdelivered water and, for example, sodium carbonate through a pipe It,for mixing therein. The fresh absorbent is pumped from the mixing tankl4 through a pipe l8 by pump 20 and through the said pipe 12 to thehereinbefore mentioned pumping tank l0. Fouled absorbent from thepumping tank ill is delivered by a pump 22 through a pipe 24 into thetop of an actifier column 26 and is distributed through nozzles 29 in adescending flow down over packing in the column. In the actifier 26 thefouled absorbent is brought into direct contact with rising,countercurrently flowing gases and vapors which 3 continuously liberatedissolved hydrogen sulphide from the fouled absorbent, and which therebyactify the downflowing absorbent.

The relatively cool fouled absorbent flowing into the top of theactifler 26 also acts as a condensing medium partially to condense steamfrom the said vapors which are produced in and rise through the actifymgcolumn.

The hydrogen sulphide and remaining steam in admixture therewith areflowed from the top of the actifier 26 through a pipe 30 into acondenser 82 wherein a larger portion of the remaining steam iscondensed. Thence the hydrogen sulphide flows through a pipe '34 to asecond condenser 36, of smaller dimenslom'in which substantially theremainder of the steam is condensed. Substantially dry technical gradehydrogen sulphide is continuously withdrawn from the said condenser 38through pipe 38 by the vacuum pump 40 by which means the entireactiilcation zone ls held under less than atmospherlc pressure and bywhich means also the hydrogen sulphide is pumped through a pipe 42 toany point for utilization thereof. Hydrogen cyanide, which is alsorecovered from the gas by the described process can be separated fromthe hydrogen sulphide by any of several known processes whereby bothsubstantially pure hydrogen sulphide and hydrogen cyanide can beobtained. Coke-oven gas flowing from a coke-oven battery 44 into onestandpipe 48 of many and thence into a collecting main 48 is cooledtherein by a spray of flushing liquor from nozzle 80. The flushingliquor having been heated by the hot gas in the collecting main 48 flowsthrough a pipe sprayed by nozzles an uponthe packing provided therein. I

Condensed steam is flowed from the said condensers 32 and 38 throughpipes 82 and 84 respectively into a pumping tank 88. Collectedcondensate is withdrawn by a pump 98 from the said tank 88 through apipe I00 and is pumped into the bottom of the absorber 4 at which pointthe condensate is mixed with fouled absorbent in order that it maysimultaneously be actifled and treated for removal of any hydrogensulphide dissolved therein.

In one instance of customary modern practice employing liquor flushingin the collecting mains, flushing liquor was sprayed into the mains atan average temperature of about 77 C. and was drained therefrom at atemperature of 78 C. In other instances flushing-liquor temperatures areas high as 85 C.. and therefore would furnish even greater heat capacityfor the present improvement. In an example of operation employing theprocess of the present invention, the flushing liquor which formerlyexhibited the said inlet and outlet temperatures of 77 and 78 C.

respectively is so-cooled by the heat exchange effected in the vacuumactiflcation zone that a new temperature of about 66 C. in the flushingliquor entering the collecting main 48 and an outlet temperature of 72C. is provided. Thus,

0 the described advantages of .facilitating the 35 fected whereby theamount of water carried by 82 to a hot settling tank 54 in whichtar-which has been condensed therewith is settled out and from which thetar is drained through a pipe 58. Flush ng liquor is decanted from thehot settling tank 54 through a pipe 88 into hot flushing liquor pumpingtank 60. The flushing liquor is pumped from the tank through pipe 82 bya pump 84, disposed therein, and into coils in a reboiler 84 located inthe base of actifler tower 28.

The coils of the reboiler 88 are immersed in absorbent solution whichcollects in the said base of the actifler column. The heat of theflushing liquor in the coils bo ls the solution in which they aremmersed and drives steam and hydrogen sulphide in an ascending va orousstream into countercurrent contact with descending fouled absorbentsolution. Absorbent solution in the b se of the actifier 28 has,therefore and by the above described step. been actified.

Cool d flu h n liquor is flowed from the reboiler through a pipe 68 intoa pum ing tank 10. whence t is pum ed by'a pump 12 in return to thecollecting main 48 through a pipe 14. The flushing liquor so deliveredto the collectin: mains is thus cooler than in customary operation: andas a resu t thereof a thinner tar is condensed in the mains, mak ng thecleaning of them easier. and the gas is cooled to a greater degree thanthat obtained by customary operation thereby relieving the load on theprimary gas-coolers of a byproduct plant.

Actified absorbent is withdrawn from the bottom of the said actifier 28through a p pe 18 and is pumped by pump 18 throu h a pi e 80 to -acooler 82 that is conventionally sup lied w th inlet and outletcooling-water pipes 84 and 88, respectively. Cooled. actifled absorbentis flowed from the sa d cooler 82 through a valved pipe 88 to the top ofthe absorber 4 into which it-is the saturated gas is reduced and itssensible heat is lowered consequently reducing to a substantial degreethe amount of cooling water required in the final coolers.

40' In an actifler operating under 3.9 to 4.5 inches mercury absolutepressure and heated by the above described flushing liquor entering thereboiler at approximately 72 C. and leaving at 66 C.', absorbentsolution is actifled and is heated from an inlet temperature of 51 C. toan outlet temperature of the actiiled solution of 55 C. The a'ctifiedsolution is cooled before being returned to the absorber and is thereheated to approximately'the temperature of the inletgas, which is about52 C.

Hydrogen sulp ide and vapors therewith, liberated in the actiiler. leavethe same at a temperature'of about 53 C. and an absolute pressure of 3.9inches mercury. It is cooled in the first condenser 32 to 38 C. and inthe second condenser 38 to 25 C. at 3.0 inches mercury. The hydrogensulphide substantially separated from its accompanying moisture isdelivered throu h the pipe 42 by the pump 40 at approxi mately 25 C. and33 inches of mercury absolute. In such an example. 12.000 gallons perhour of foul solu ion are actiiled by a vapor rate (of vapor boiled onthe'actiiled'solution by the heat of the flushing liquor in thereboiler) of i 830 000 cubic feet per hour, and 18200000 cub c feet ofgas is treated for removal of 7200 pounds of hydrogen sulphide per day.

r In the above iven example. 8. 300000 B. t. u'. are required for vacuumactification'. Heretofo e. the industry has not conside ed the heat offluids eilluent of the collec in mains utilizable because of their lowthermal head which is such tha only small portions of their heat wouldordinarily be transferable. W th the present invention the heat supplyhas been found to be adequate from this source. With a liquor flushingrate of 105,000 gallons per hour as in the above example a cooling ofthe flushing liquor in the actification zone of only C. will furnishsuflicient heat for the purification of all of the coke-oven gas by theabove process.

In certain instances it may be preferred to heat actified solution,under mild pressure, by indirect contact with flushing liquor, and thenconduct the heated solution to the vacuum actification zone whereinheated solution vaporizes, passes through the fouled solution, andactifies the same. In such method, the flow-rate of actified solutionthrough'the heat exchanger is several times the rate of withdrawal ofactified solution being returned to the absorber, in order thatsufficient vapors are provided to ensure adequate actification.

In other instances the flushing liquor can itself be vaporized byflowing it into a zone of low pressure. The so-formed water vapors canthereafter be passed countercurrently through the fouled absorbent toliberate absorbed constituent therefrom. Whether flushing liquor, orother efliuent, is employed directly or indirectly its heat is utilizedto form water vapor from itself or the absorbent, which will sweepabsorbed constituent from the fouled absorbent.

The herein described invention can be employed to improve the eiilciencyof any process for liquid purification wherein the fouled liquidabsorbent containing a, constituent which has been scrubbed from a gasor extracted from a liquid is actiflable under subatmospheric pressureby heating the same. An example of a liquid purification process similarto the one herewith described comprises the use of water to absorbammonia and hydrogen cyanide from raw cokeoven gas, the water containingthe absorbed gases being thereafter actiflable by heating atsubatmospheric pressure Aqueous absorbents can be, for example, water oraqueous solutions of potassium, sodium, or other alkali metal carbonatesand bicarbonates, solutions of alkali-metal salts of other weak acids,or solutions of weak bases such as organic amines. The absorbableconstituent in coke-oven gas, or coal gas, can

be hydrogen sulphide, hydrogen cyanide, carbon dioxide, ammonia, lightoil, or carbon disulphide. The light oil and carbon disulphide can berecovered by scrubbing coke-oven gas with a straw oil and the light oilbe stripped therefrom, under vacuum,by heat from the said eiliuentfluids. Such light oil for, example can be purified in respect ofremoval of its hydrogen sulphide content by extraction of it with analkaline aqueous solution which can thereafter be regenerated undervacuum by the low-temperature. heat recoverable from the describedeilluent fluids.

The invention as hereinabove set forth is embodied in particular formand manner but may be variously embodied within the scope of the claimshereinafter made.

l. A process for separation and recovery of hydrogen sulphide, and thelike, from coke-oven gas. comprising: scrubbing the coke-oven gas withan alkaline aqueous absorbent and absorbing drogen sulphide and the likefrom coke-oven gas,

comprising: scrubbing the gas with an alkaline aqueous absorbent andabsorbing hydrogen sulphide therefrom; removing fouled absorbentcontaining the dissolved hydrogen sulphide from the absorption zone andflowing the same through an actification zone under less thanatmospheric pressure; circulating actified solution from theactifioation zone into indirect contact with hot flushing liquoreffluent of a collecting main of a coke-oven battery and by heatinterchange therewith heating the actified solution; expanding theheated solution into the actiflcation zone to generate vapors which passinto direct contact with fouled absorbent and liberate therefrom gasesincluding hydrogen sulphide; removing hydrogen sulphide from theactification zone; circulating so-cooled flushing liquor in a closedcycle between the actiflcation zone and the collecting main andreturning actified solution, in closed cycle, to the absorption zone.

3. In a continuous process for the separation and recovery of hydrogensulphide from cokeoven gas, in which process coke-oven gas is scrubbedwith an aqueous solution of alkali-metal carbonate and hydrogen sulphideis absorbed thereby and dissolved in solution, and in which the fouledabsorbent is thereafter actified by heating at less than atmosphericpressure, the

improvement comprising: continuously flowing absorbent and liberatinghydrogen sulphide from the fouled absorbent.

hydrogen sulphide therefrom; removing fouled HERBERT A. GOLLM'AR.

REFERENCES CITED The following references are of record in the file ofthis patent:

I UNITED STATES PATENTS Number

